DESCRIPTION: The long-term goals of this research is to elucidate the mechanisms of molecular motors. The current proposal attempts to are to identify the structural elements which are responsible for the powerstroke in skeletal muscle myosin by using novel resonance energy transfer probes that can measure long distances separating the two probes with accuracies on the angstrom level. These probes have been synthesized in Dr. Root's laboratory and will be applied to the following specific aims: 1) Test existing atomic resolution models of rigor myosin subfragment-1 binding to actin under solution conditions. 2) Determine if internal bending of myosin in the presence of nucleotide analogs is sufficiently large to account for the powerstroke. 3) Investigate alternative sources of the powerstroke such as myosin rotation on the actin filament and possible contribution of actin to the powerstroke. 4) Examine the differences in the contributions of the two myosin heads by comparing the orientation of binding to actin of single-headed myosin versus double-headed myosin. The findings of these studies will contribute to more unified biochemical and structural models of mechanisms of motor proteins. Such models will provide a basis to evaluate diseases that are really caused by structural defects in molecular motors, for example, familial hypertrophic cardiomyopathy.